1. Field of the Invention
The present invention relates to a parallel computer system and more particularly to a storage device access system for performing access to a disk apparatus of a computer equipped with a disk apparatus from a computer system not equipped with a disk apparatus and to a storage apparatus access system for distributing and synthesizing data, when a disk apparatus is accessed in a parallel computer system comprising computers equipped with disk apparatuses and computers not equipped with disk apparatuses.
2. Description of the Related Art
In science and technology calculations, such as in graphic processing, parallel computer systems have been widely used, and most recently parallel computer systems comprising more than 1000 computers have been used.
In a parallel computer system comprising a plurality of or many computers (cells), it is inefficient from the view point of hardware and resources for all the computers to be provided with an external memory such as a magnetic disk apparatus. There are many parallel computer systems that comprise computers equipped with disk apparatuses and computers not equipped with disk apparatuses.
In these computer systems it has become necessary for the computers equipped with disk apparatuses to merge data transmitted from the plurality of other computers to store data in their disk apparatuses, and to then divide the data read from the disk apparatus into a plurality of data and send them to the plurality of other computers.
In this case, conventionally, the data transmitted through a network from a plurality of computers are stored once in a memory of a local computer, and the data stored in the memory are merged when all the data are received. They are then written into the disk apparatus in a single block. A group of data transmitted from the disk apparatus are stored once in the memory, and thereafter read and distributed from the memory and transmitted to a plurality of computers through a network.
As described above, after data are read into the memory from the disk apparatus, they are written into the memories of respective cells forming a parallel computer system, or are transmitted to the network. Therefore, there is a problem in that there is overhead in temporarily copying the data from the disk apparatus to the memory. The data received from the network are temporarily written into the memory and thereafter written into the disk apparatus in a group. This creates additional overhead in synthesizing the data in the memory. In particular, where the data are uniformly and regularly distributed to be written into memories of a plurality of cells or are to be transmitted to many cells through the network, the longitudinal lines 1, 2, 3, 4, 5 . . . of the image data are sequentially assigned to a total of nine cells, cell 1, cell 2, cell 3, cell 4, cell 5, cell 6, cell 7, cell 8, and cell 9, to write the image data into the memories of the cells or to transmit the data to the cells through the network. In this case, it is necessary to repeat the operation of writing the data into the memory of the same cell at predetermined intervals (such as every ninth time) or the operation of transmitting the data through the network to the same cell at predetermined interval. Therefore, if the data are distributed to respective cells after they are read into a memory of a particular cell from its disk apparatus as a group, considerable overhead is created. Considerable overhead is also created if, conversely, the data are written into the disk apparatus as a group after the partial data read from the memories of many cells or the partial data received via the network are all merged on the memory of the particular cell.
When the data are transmitted from a computer without a disk apparatus, namely, a cell without a disk, to a computer with a disk apparatus, namely, a cell with a disk, or data in a computer with disk apparatus are accessed by a computer without the disk apparatus so that the data are read therefrom, conventionally the computer without a disk issues a disk access request to a file server of the cell with the disk, and the file server accesses the disk and sends a response to the cell without the disk, or returns the data to the cell without the disk.
Where a cell without a disk accesses the disk apparatus of a cell with a disk, the file server operates on the side of the cell with a disk, thus delaying the execution of the user task of the cell with the disk. When the cell with the disk executes a user task with high priority, the user task issuing the disk access request on the side of the cell without the disk is kept waiting longer than necessary.